A goal of prosthetists has been to reduce the weight of below-knee prostheses to reduce the energy and hence fatigue of the wearer. Reduction in weight, however, has to be balanced with the need to maintain sufficient weight-bearing strength to support the wearer during normal activity levels. The various materials used in the prior prostheses, such as wood and alloy metals (e.g. titanium), also tended to be rigid. This lack of material flexibility did not allow significant energy storage and return during activities such as walking or running which, in turn, detracted from a natural feel to the wearer of the prosthesis.
The most common artificial leg for below-knee (b.k.) amputees are of a rigid nature. A solid shank will connect the socket, which mounts the artificial leg to the residual limb of the amputee, and the artificial foot. The shank is often made out of a rigid alloy such as one containing titanium or is made from shaped wood. The attachment of the shank to the artificial foot is also usually rigid. While advances have been made in the construction of artificial feet to provide energy-storing/releasing systems, these advances primarily have the energy-storing system contained within the foot itself and not able to store energy through the shank due to the termination of the energy-storing system at the rigid foot-shank union. The energy-storing system can take the shape of a C-shaped plastic spring running from the ankle through the arch and terminating toward the ball of the foot. In the case of the metal shanked artificial leg, the system can weigh in the range of 31/4-4 pounds. In the case of the wood shank, the artificial leg can weigh on the order of 3 pounds.
The Flex-Foot.RTM. artificial leg produced by Flex-Foot, Inc., Irvine, Calif., is an example of the currently available artificial leg which exhibits a more natural dynamic action by using a flexible energy storing pylon and keel, the flexible pylon and keel being formed from a strip of laminated reinforced composite which is mechanically attached to the socket descending down to form the pylon and continuing on to form the keel of the artificial leg. Applying pressure to the Flex-Foot.RTM. artificial leg (e.g. Walking on it) causes flexation of the pylon and foot which acts as a spring to store energy and release it during walking or running movements. While the Flex-Foot.RTM. artificial leg allows for more natural-feeling movement due to its energy storing and returning action than prior rigid artificial legs and while lighter than other prior art legs made of titanium and/or wood, its weight (on the order of approximately 21/4 pounds) can be of concern to geriatric patients, as well as more active patients.
For geriatric patients, artificial legs of these weight ranges can cause discomfort and reduced activity. Oftentimes small savings in weight can produce great results due to the nature of walking with its repeated activities of lifting the leg. Likewise, for younger amputees, the increased weight can cause increased fatigue during exercise and slower times when competing e.g. in races. The prior art also suffers from a lack of flexibility which would allow sufficient energy storage and return to approximate the dynamics involved in athletic activities such as running.
The invention provides a prosthesis with improved energy storage and return action. The invention also provides a prosthesis that is substantially lighter than known prostheses while still offering sufficient weight-bearing strength. The invention further provides a prosthesis that is readily capable of having its energy storage and flexation action modified. The invention provides a durable prosthesis which provides an energy storage and return action for the wearer. The invention provides a prosthesis which can be easily fabricated by trained personnel using readily available orthopaedic materials and commonly available equipment.
From the subsequent detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.